1. Field of the Invention
The present invention relates to an adaptive high-frequency filter device to be used primarily in a high-frequency section of wireless apparatuses such as cellular telephones, an adaptive filter device combined to a transmit-receive antenna, and a wireless apparatus using those devices.
2. Prior Art
In recent years, it has been practiced that in simultaneous two-way wireless communication apparatuses such as cellular telephones and car telephones used in cellular wireless communication systems, a filter device is provided between a transceiver and its antenna. In this wireless communications system, available frequency bands are assigned to a transmitting frequency band and a receiving frequency band, and the filter device is equipped with, on the receiver side, a filter device that allows the passing of a receivable frequency band and, on the transmitter side, a filter device that allows the passing of a transmittable frequency. In communications apparatuses for use in this system, in recent years, there have been exploited frequency-shift type filter devices in which each of a frequency band for reception use and a frequency band for transmission use is divided into two so that the filter device is enabled to switch between the divided smaller frequency bands.
Japanese Patent Publication No. 11-243304 discloses an example of filter devices of frequency-shift type. As shown in FIG. 9, this filter device comprises a receiving filter device and a transmitting filter device which are combined at a single antenna terminal and connected in series. In the combined filter device, the transmitting filter device has its transmitting terminal 94 connected to a final stage of the transmitter, the receiving filter device has its receiving terminal 95 connected to a high-frequency stage of the receiver, and an antenna terminal 96 is connected to a common-use antenna circuit.
Each filter device of the combined device is formed of two- or three-stage filters, each of which includes a dielectric resonator 91 which is, in common, grounded at one end, where a capacitance 93 is connected in parallel to the dielectric resonator 91 via a PIN diode switch 92 which turns on or off the parallel capacitance 93 to switch the resonance frequency.
The filter device, generally, includes a band pass filter and a band elimination filter. In one of the band elimination filters as shown in FIG. 9, an input or output terminal is connected to a notch coupling capacitance 97 and a resonator 91 in series, the resonator being grounded, and also to a loading capacitance 99 being grounded, while the input terminal is connected to an output terminal via an interstage coupling inductor 98. For the makeup of a filter device including multi-stage filters, these filters are connected in series, each having a different resonating frequency.
In the other band pass filter, input and output ends are made up so that an inter-stage coupling capacitance 910 and an input-output coupling inductor 911 are connected in series, and that the resonator 91 having one end grounded is connected to this capacitance 910 and inductor 911. A branch coupling capacitance 912 is connected between the input and output ends in a parallel fashion. These filters are connected in series to make up a multi-stage band pass filter.
These two filter devices (i.e., transmitting filter device and receiving filter device) are connected in series at an antenna terminal, sharing the antenna terminal. For connection to a common antenna used in a simultaneous transmit-and-receive apparatus, the filter devices are connected to the antenna terminal via an L-type matching circuit of an inductor 913 and a capacitance 914 for matching purposes, thus forming a filter device for common use of both transmitter and receiver of the above apparatus.
In such a frequency-shift type filter device for common use with a high-frequency antenna, the dielectric resonator 91 is provided with the capacitor 93 in parallel via the PIN diode switch 92 as shown in FIG. 9, wherein the resonance frequency of the resonator 91 can be selectively switched between a low frequency f1 and a high frequency f2 by electrically turning on and off the PIN diode switch 92. In the example shown in FIG. 9, the receiving filters and the transmitting filters each use a resonator changeable resonance frequency. One filter device generally uses two or more filters for switching their respective resonance frequencies, resulting in switching the center frequency of the filter band.
This filter device has advantages so as not to be necessary to lower the pass loss throughout the whole passband, or to increase the attenuation ratio throughout the whole attenuation band. Therefore, each of the two filter devices are only required to cover a half of the whole band, thereby reducing the burden of the filter device. That is, this can exhibit the same effect, apparently, as the transmit and receive frequency gap of the filter expanded by a half of the entire passband.
Japanese Patent Publication No. 2000-312161 discloses the concept that a wireless apparatus changes the attenuation amount of the filter depending on nations or regions where the apparatus is used by detecting positional information with other communication means such as signals transmitted from a base station or GPS.
In the above filter devices, to decrease the burden of the filter with attenuation characteristics covering the whole bandwidths for transmission and reception in a communication system, the filter characteristics are changed to be applicable to the communication frequency bands that are differently allotted for the country in which the wireless apparatus is used.
Further, FIG. 10 shows a structure of an actual prior-art wireless apparatus, such as a portable cellular telephone, including filter devices for a transmit-receive antenna. The apparatus includes a semiconductor integrated circuit 103 provided with a wireless circuit, a filter device 101 which is connected to the semiconductor integrated circuit 103, and an internal antenna 102 which is coupled to a dielectric filter device 101, these being mounted on, or formed in, a printed circuit board 104, and an external antenna 106 is also provided which is connected to the filter devices 101. This wireless apparatus is large in number of parts, difficult to manufacture, and also occupied in great deal by the wireless section.
The prior art filter devices have only been capable of changing the filter band frequency, alternatively and simply, to either one of two frequency passbands, subordinate to frequency selection of transmitting signals and received signals.
The technique of changing the attenuation amount based on detected positional information has not provided sufficient characteristics for the filter.
Further, the wireless apparatuses for simultaneous bi-directional wireless communication have been insufficient to protect against interfering waves other than an under-reception target signal under actual wave environments in which the wireless apparatus is used, as well as to suppress spurious signals issued by the apparatus itself during signal transmission. Thus, the characteristics of antenna-coupled filters are required to be changed adaptively in response to the change of wave environments around, and the operating state of, the wireless apparatus in use.
In order to completely prevent such interfering waves and unnecessarily radiated waves, the conventional filter devices in which passband frequencies are fixed had to involve ultra-high filtering performance characteristics, necessitating multi-stage high-Q resonators, in which case the filter devices would be required to have a large size. Downsizing the resonators to downsize the filter device would cause the high-frequency characteristics to deteriorate, not obtaining practical, required characteristics.
Furthermore, from the viewpoint of the configuration of parts in such actual filters mounted, filter devices have been difficult to manufacture because of the large number of component parts, which occupy quite a large area of the wireless section.
An object of the present invention is to provide an adaptive high-frequency filter device that is small in size and high in performance and is capable of adaptively changing and controlling the frequency characteristics of filters according to ambient wireless environments or the operating state of the wireless apparatus.
Another object of the invention is to also provide a high-frequency filter device in which component parts constituting the filter device are integrated by using multilayer techniques.
The present invention further provides a wireless apparatus being integrated with a filter device to be downsized.
The high-frequency filter device of the present invention includes at least one filter to be connected to a high-frequency stage of a wireless apparatus, the at least one filter comprising a voltage-controlled variable frequency resonance element which comprises a resonance element and a voltage-controlled variable impedance element electrically connected to the resonance element. The high-frequency filter device includes a control section for controlling a voltage applied to the variable impedance element, and a signal monitoring section for outputting a control signal, with which the voltage is controlled, to the control section based on frequency data as to an oscillating frequency of a local oscillator of the wireless apparatus. The signal monitoring section controls a band frequency of the at least one filter based on the frequency data in a manner such that the band frequency is continuously varied.
In the filter device of the invention, the resonance element may be a distributed-constant TEM mode resonator. Preferably, the resonance element is implemented by a stripline resonator arranged in a laminate dielectric or on a surface thereof.
In this apparatus, the voltage-controlled variable impedance element is a variable capacitive or inductive element, preferably, a variable capacitance circuit, and particularly preferably, a circuit using a varactor diode.
The variable frequency resonator may be made up by connecting in parallel a stripline resonator and a varactor diode for controlling by a variable voltage signal, an additional, variable capacitance to be added to the resonator, and then controlling the band frequency of the filter.
In the present invention, the high-frequency filter device may include at least one band pass filter using the variable frequency resonator. The filter device may, also, include at least one band elimination filter using the variable frequency resonator. The filter device may further include a combination of a band pass filter and a band elimination filter.
In the high-frequency filter device of the invention, the signal monitoring section variably controls the band frequency of the at least one filter based on the frequency data so that a passband of the filter can include a pass frequency of the high-frequency stage of a receiver and/or a transmitter in the wireless apparatus.
It is also possible that the signal monitoring section further detects radio signals toward and/or from an ambient wave environment around the wireless apparatus and transfers a control signal to the control section so that the at least one filter reduces unnecessary or interfering waves, and that the control section generates a control voltage signal to variably control the band frequency of the at least one filter.
The wireless apparatus using the filter device of the present invention may include a transmitter and/or a receiver. When the wireless apparatus includes at least a receiver, the at least one filter is connected between a high-frequency amplifying stage of the receiver and an antenna, and the at least one filter includes a band pass filter for reception and a band elimination filter for reception. The signal monitoring section for reception monitors unnecessary interfering signals in the received signals by the wireless apparatus and generates a control signal for reception by an adaptive control algorithm. The control section controls the band elimination filter by a control voltage signal based on the control signal so that an elimination band of the band elimination filter maximizes a ratio of a desired received signal to interfering waves.
When the wireless apparatus includes a transmitter, the at least one filter of the high-frequency filter device includes a band pass filter for transmission and a band elimination filter for transmission, the signal monitoring section for transmission, while monitoring unnecessary spurious signal waves of a transmitting signal of the wireless apparatus, generates a control signal by an adaptive control algorithm, and the control section for transmission controls the band elimination filter by a control voltage signal based on the control signal so that an elimination band of the band elimination filter for transmission minimizes unnecessary spurious waves included in the transmitting signal.
The filter device, combined with a transmit-receive antenna, comprises a high-frequency filter device for transmission including transmitting filters to be connected between the transmit-receive antenna and a transmitter of a wireless apparatus, and a high-frequency filter device for reception including filters to be connected between the antenna and the receiver, wherein the transmit-receive filters include the respective voltage-controlled variable-frequency resonance elements, each of which comprises a resonance element and a voltage-controlled variable impedance element electrically connected to the resonance element. The filter device for a transmit-receive antenna includes a control section for controlling a voltage applied to the variable impedance elements, and a signal monitoring section for outputting a control signal, with which the voltage is controlled, to the control section based on frequency data as to an oscillating frequency of a local oscillator of the wireless apparatus, and the signal monitoring section controls band frequencies of the transmitting filter and the receiving filter based on the frequency data in a manner such that the band frequencies are continuously varied.
In such a filter device for a transmit-receive antenna, the transmitting filter has a first passband and a first elimination band, and the receiving filter has a second passband and a second elimination band. The signal monitoring section controls the first passband and the first elimination band so that their band frequencies are synchronously varied with their frequency interval kept constant, and controls the second passband and the second elimination band so that their band frequencies are synchronously varied with their frequency interval kept constant. Further, the first passband and the second elimination band become generally coincident with each other and the first elimination band and the second passband become generally coincident with each other.
In such a high-frequency filter device for a transmit-receive antenna, the signal monitoring section further detects a radio signal toward and/or from an ambient environment of the wireless apparatus and transfers a control signal to the control section so that the at least one filter reduces unnecessary or interfering waves, and the control section generates a control voltage signal to variably control the band frequency of the at least one filter.
In the high-frequency filter device for a transmit-receive antenna, the signal monitoring section monitors unnecessary interfering signals of a received signal of a receiver of the wireless apparatus and generates a control signal for reception by an adaptive control algorithm, and the control section controls the band elimination filter by a control voltage signal based on the control signal so that an elimination band of the band elimination filter of the receiving filter maximizes a ratio of a desired received signal to interfering waves.
Also, the signal monitoring section, while monitoring unnecessary spurious signals of a transmitting signal of a transmitter of the wireless apparatus, generates a control signal for transmission by an adaptive control algorithm, and the control section for transmission controls the band elimination filter by a control voltage signal based on the control signal so that an elimination band of the band elimination filter for transmission minimizes unnecessary spurious signal waves of the transmitting signal.
The present invention further includes a wireless apparatus which includes the high-frequency filter as described above, wherein the at least one filter is connected to an antenna circuit.
The present invention also includes a wireless apparatus which includes the filter device for a transmit-receive antennas as described above.
The high-frequency filter devices and the filter devices for transmit-receive antenna according to the present invention are used at relatively high frequency regions, for example, RF and microwave bands of frequencies higher than the shortwave band. Such wireless apparatuses can suitably be applied to, not only receivers and transmitters of the one-way communications system, but also transceivers for the simultaneous two-way communication system, in particular, portable telephones in the cellular communications system.